Synovial joints are the most common joints of the mammalian appendicular skeleton, representing highly evolved, movable joints. A typical synovial joint comprises two bone ends covered by layer of articular cartilage. The cartilage is smooth and resilient, and facilitates low-friction movement of the bones in the joint.
The bone ends and associated cartilage are surrounded by a joint capsule—a “sack” of membrane that produces synovial fluid. The capsule and fluid protect and support the cartilage and connective tissue, carrying nutrients to the articular cartilage and removing the metabolic wastes.
The articular cartilage is a thin (2-3 mm) layer of hyaline cartilage on the epiphysis of the bone. It lacks a perichondrium, and thus has a limited capacity for repair when damaged. Additionally, the natural aging process can cause the articular cartilage to degenerate somewhat, reducing its capacity to protect and cushion the bone ends.
Zygapophysial joints, better known as facet joints, are the mechanism by which each vertebra of the spine connects to the vertebra above and/or below it. Each joint comprises two facet bones—an inferior facet and a superior facet—with the inferior facet of one vertebra connecting to the superior facet of an adjacent vertebra. The joints facilitate movement of the vertebra relative to each other, and allow the spine to bend and twist.
As in all synovial joints, where the facets contact each other there is a lining of cartilage lubricated by a thin layer of synovial fluid. The cartilage and synovial fluid decrease friction at the joint, extending joint life and preventing inflammation and associated pain.
As the natural aging process progresses, the cartilage covering the joint may deteriorate and start to fray. The fraying process may cause pieces of cartilage to break free, and the previously smooth surfaces may become rough. The facet bones then begin to rub together, creating friction which leads to further deterioration of the joint. Moreover, the nerves associated with the joint become irritated and inflamed, causing severe pain and restricting movement of the spine.
Techniques for addressing degeneration of synovial joints in general, and facet joints in particular, joint have heretofore relied primarily on injections to block pain and reduce inflammation. This treatment is only temporary though, and rarely leads to any significant improvement of the underlying condition.
A need therefore exists for materials and methods effective for treating degenerating synovial joints, and particularly for materials and methods effective for supplementing or replacing the cartilage that lubricates and protects the joint. The present invention addresses that need.